A brief earthquake (search) struck the Midwest early Monday, rattling windows and awakening sleeping residents from Wisconsin south to Missouri and from Indiana west to Iowa.

No injuries were reported from the quake, which occurred about 1:11 a.m. CDT.

Brian Lassige, a geophysicist with the U.S. Geological Survey (search) in Colorado, said the quake was magnitude 4.5, and its epicenter was about eight miles northwest of Ottawa in northern Illinois, close to the small village of Troy Grove (search). The rural area is about 70 miles west of Chicago.

Initial reports indicated no major damage from the temblor, although police agencies and radio stations within the quake area were inundated with telephone calls.

"It was mayhem around here for a while," said Pattie Burke, a dispatcher for the Ottawa Police. "We had more than 200 calls from residents in a short period of time, all of them wanting to know what had happened. A lot of them seemed to think a truck had crashed into their house.

"Here in the station, it felt like an aircraft was about to crash right here."

The quake was felt at three nuclear power plants in Illinois: Quad Cities, LaSalle and Dresden.

Craig Nesbit, a spokesman for the Exelon Corp., which owns the three generating stations, said the Nuclear Regulatory Commission (search) declared an "unusual alert" for all of them, although there appeared to be no damage.

"All of them were operating 100 percent, and no problems were reported, but we did a check of all safety systems," Nesbit said.

Nesbit said the three stations supply electrical power for several million Illinois residents.

Reports of the shaking came from at least as far east as Valparaiso, Ind., and as far west as the Quad Cities, and from Wisconsin in the north to the St. Louis area in the south.

Gary Spaulding of Marseilles, Ill., said he was relaxing in his mobile home when the quake struck.

"It was like somebody shot off dynamite," said Spaulding, who added that his cat leaped out of his lap and would still not come near him two hours later. "I thought maybe a tree hit my trailer."

Joe Knapp of Delafield, Wis., just west of Milwaukee, said he was asleep and awoke when the bed began shaking. "Everything was just rolling back and forth," Knapp said.